HHH-21002 Handle JSON-B API without a provider

[lucamolteni]

Summary

• Handle an API-only JSON-B classpath during automatic mapper discovery by returning no mapper when provider discovery reports a missing provider.
• Use standard JSON-B provider discovery, while retaining fail-fast behavior for explicit JSON-B mapper construction and failures when an installed provider creates its builder or JSON-B instance.
• Add isolated-classloader regression coverage for a missing API, an API without a provider, an installed provider, explicit mapper construction, and a failing provider.

Jira: https://hibernate.atlassian.net/browse/HHH-21002
Reported in quarkusio/quarkus#57388.

Verification

• ./gradlew formatChecks :hibernate-core:test --tests org.hibernate.orm.test.type.format.JakartaJsonIntegrationTests --tests 'org.hibernate.orm.test.mapping.basic.JsonMappingTests$*' passes: 24 focused tests on both main and 8.0.
• The API-only regression test fails before the fix and passes afterward.
• The same fix on ORM 8.0.0-SNAPSHOT successfully builds the Quarkus issue's native reproducer with local Quarkus 999-SNAPSHOT and GraalVM CE 25.0.2, without adding Yasson or quarkus-jsonb. The original build with ORM 8.0.0.Beta3 fails during native-image analysis.

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Please make sure that the following tasks are completed:
Tasks specific to HHH-21002 (Bug):

• Add test reproducing the bug
• Add entries as relevant to migration-guide.adoc OR check there are no breaking changes

[marko-bekhta]

thanks 🙂 makes sense 👍🏻

[marko-bekhta]

maybe try looking at @ExtendWith(ClassLoadingIsolaterExtension.class) ? (I'd rather we try keeping those CL sort of tests using the same infra if possible 🤞🏻🙂)

[marko-bekhta]

Suggested change

	catch (JsonbException e) {
	if ( e.getCause() instanceof ClassNotFoundException ) {
	// The API is available, but its default provider is not.
	return null;
	}
	throw e;
	catch (JsonbException e) {
	log.debug(...,e);
	return null;

the docs only seem to talk about JsonbException so maybe let's just log and move on ?

[github-actions]

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[sonarqubecloud]

Quality Gate failed

Failed conditions
0.0% Coverage on New Code (required ≥ 80%)

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